Pressure fluid operated tool



Jan. 16, 1940. E. H. sHAFF PRESSURE FLUID OPERTED TOOL Filed Feb. 27, 1936 2 Sheets-Sheet l @Ch-Tonini aye Jan. 16, 1940; E H, SHAFF 2,187,502

PRESSURE FLUID OPERATED TOOL Filed Feb. 27, 1936 2 Sheets-Sheet 2 .J/ f m' 70 f 6`-fnoveltool of the above character so constructed.

Patented Jan. 16, 1940 PATENT OFFICE PRESSURE FLUID OPERATED TOOL Ernest H. Shaif, Grand Haven, Mich., assignor to William H. Keller, Inc., Grand Haven, Mich., a corporation of Michigan Application February 27, 1936, Serial No. 65,983

11 Claims.

This invention relates to pressure iuid operated tools and more particularly to a new and improved portable tool of the hammer type.

One object of the invention is to provide a asvto prevent stalling of the impact piston.

Another object is to provide ina tool of the character indicated, a valve mechanism of novel I and improved construction insuring ease in start- `inggancl improved high-speedoperation o f the tool.

Another object is to provide anew and improved tool in which the recoil shocks yand vibrations"customarily incident to operation of the tool are cushioned and substantially prevented from transmission'to the handle, thereby increasing the efficiency of the tool,` decreasing the breakage hazard and rendering the tool safer and less fatiguing in use.

In the, attainment of these objects the tool embodies avalve mechanism in which a disk valve fof substantially wafer` thinness and having an entremely short range of movement isadapted to control vefectually the now of pressure iluid to opposite ends of the Ipiston chamber so as to effect rapid reciprocal movement 'of the *impact piston, and means coacting with the valvemaintans "apermanently unbalanced pressure condition on one side of the valve to eliminate entirely :any possibility of the tool stalling dueto equalizationof` pressure. Furthermore' the `tool embodies a new and improved cushioning construction utilizing in combination the shock 4absorbing qualities of'mechanical means and compressible pressure fluid. f

Another object resides inthe improvements in construction and the novelprelationships of parts by which the foregoing and other objects and advantages oi the invention may be carried into practice simply and economically.

Other. objects and advantages will become apparent from the following description taken in connection with the accompanying drawings, in`

which:` v

Figure l is a longitudinal 4sectional vie'w through a tool embodying the principles of the invention, thevalve being `shownin the position it occupies during the forward stroke of the piston.

HFig. 2 is afragmental sectional view of the rear end of the tool'taken on asimilar plane as Fig. l

but 'showing the valve in the position it assumes during the rearward movement of the piston and also showing the parts of the tool in the relative positions they occupy when the cushioning means is iniull operation.

Fig'. 3 is a perspective assembly View of the valve mechanism showing the face of the rear valveecasing member.V y

. lig. 4 is a sectional plan view taken substantially on the planeof line 4 4 of Figi.

Fig. 5 is a sectional plan view taken substantialiy along the plane of line 5--5 of Fig. l.

'While the invention is susceptible of various modifications and alternative constructions, I have shown in the drawings andwill herein de scribe in detail the preferred embodimentybut' it is to be understood that I do not thereby intend to limit the invention to the specific form dsclosed, but intend to cover allmodifications and alternative constructions falling within the spirit and scope of the invention as expressed in the appended claims.

The tool shown in the present instance is oi the type generally referred to as a chippinghammer which comprises an elongated barrel I having a chamber l2 'for a piston i3. An im pact tool I4 is carried by the forward end of the barrel; and at the rear end of the barrel is a Valve mechanism, indicated generally by the numeral l5. Pressure fluid may be supplied in the usual manner through a valve controlled passage vIl' in a handle portion I8 and serves to `reciprocate the piston which during its reciprocatory `movement controls the exhaust of pressure fluid from the piston chamber.

While in the preferred construction, the valve mechanism l embodies substantial improve ments, it may be of generally similar form andA operation as setforth in the H. Shai Patent No` 1,924,812 issued August 29, 1933. Accordingly it comprises a cylindrical casing made from two coaxially alined members in the form of circular plates I9 and 20 held in a predetermined iiXed relation by dowel pins 2| which fit infcomplementary holes 22 in the piates (see Fig. 8). The opposed faces of said plates are recessed to provide therebetween a valve chambert having forward and rear faces 24 and 25, respectively, and said faces are spaced apart a distanceonly slightly greater than the thickness of a substantially Wafer-thin, reciprocable disk valve 25 which is enclosed therein. A

The assembled valve casing is preferably of greater diameter than the piston chamber l2 and. is supported in closing relation to the rear end of the latter. For this purpose, the rear end oil the barrel l0 has an enlarged portion or head 21 projecting beyond the piston chamber and having a'bore 28 of a diameter to receive the valve casing l5, The latter is held against a shoulder 29 ywith the supply ports 33.

at the forward end of the bore 23 by suitable means such a ring nut 3B threaded into the rear end of the bore and coacting with the rear face of the casing plate I9. To hold the casing against turning, the forward ends of the dowel pins ZI engage with holes 22a (see Fig. 3) in the shoulder 2S. ln its rear face, the ring nut is provided with wrench sockets 3 I.

For delivering pressure fluid'fromtthe passage I 7 in thehandle to the valve chamber a pressure uid port 32 opens from the passage il toward the rear face of the casing plate I9, and the f latter is equipped with a plurality of supply ports 33 disposed adjacent the periphery of the valve chamber.

- The forward face of the valvel chamber has a plurality of shallow circular recesses34 coaxial By alining 'the axes of these ports and recesses substantially with the peripheral surface of the disk valve 2.6', pressure iiuid may be admitted to the Valve chamber upon either side of the valve, depending on the posi,- tion of the latter with regard to the respective faces of the valve chamber.

When the disk valve 2G is in its rearward posi-k tion, shown in Fig. l, the pressure fluid will pass to the forward side of the valve chamber for delivery to the rear end of the piston chamber I2 stantially the same distance from every adjacent,

by means'of a plurality of inlet ports 35 (herein seven in number) provided in the 'forward valve plate 2D. f

-In order. to provide maximum operating effi-k ciency by affording the greatest practicable inletA inlet port. As shown, there may be seven of the inlet ports 35, all equally spaced apart and their combined inlet area permitting free and eicient passage yof pressure fluid into the rear end of the piston chamber I2. Thisarrangement of the inlet ports alsor permits reduction to a minimum of the necessary movement of the disk valve 2S away from the forward face of the valve chamber to admit the requisite volume of pressure uid to the piston chamber.

`For the purpose of permitting movement of the disk valve 26 away from the forward face of the valve chamber with utmost rapidity and with the least fricticnal or vacuumdrag, conf` tact between the valve and the face should be exceedingly limited. Practically this end may be attained by the provision of very narrow annular flanges or rims 3l individually surrounding the inlet ports S5. rlhese rims serve to maintain the.V

valve disk spaced from the major area of the forward face 24 when the Valve disk is in sealing relation to the ports,. The internal diameter ofv Vthereagainst during operation of `the tool.

Through this construction, the sensitivity k,of the valveis greatly increasedbecause-a continuous air cushion is maintained over the major area of the forward chamber face 24, thus facilitating unsealing movement of the valve.

Pressure iiuid for kreturning the piston I3 toward the rear of the barrel after impact with the tool I4, is delivered in the usual manner to the forward end of the piston chamber I2 through delivery ports 38 which communicate with a plurality of elongated passages 39in the wall of the barrel. At their rear endsr the'passages 39 open into the valve mechanism I5 through angularpassages 40 which `are formed in the casing members I 9 and 2li and which open into the rear side of the valve chamber 23 through inlet ports 42 in the rearwall of the chamber', two such inlet ports being provided in the present instance.

l Where the rear Valve chambery face concentrically surrounds the ports 42 it is quite smooth to coact sealingly with the rear face of the valve disk 26, but the total area of Contact between small quantities of air are apparently trapped.

in such recesses 43.` Inany event it has been found that this construction insures instantanecus movementof the valve to-unsealing position, tl'lus counteracting 'any tendency of the valve to cling to said face. v

Recipr'ocation of the piston I3 is `effected in the manner described in the aforesaid Shai Patent No. 1,924,812, pressure iiuid being admitted by the disk valve 2S alternately to the rear or the front of the piston chamber through the inlet ports or 42, respectively. The valve 26 is movable for this purpose under the control of the piston in response to pressure variations or inequalities developedin the .piston chamber f on the opposite sidesof the piston. vIn its cycle of movement, the piston alternately opens orv closes forward or rear exhaust ports 44 and 45, respectively, which are suitably spaced longitudinallyvr of the piston chamber as is customary. Exhausted pressure iiuid is passed to atmosphere through longitudinal exhaust passages, 41`in the wall ofthe barrel communicating with the exhaust ports 44 and 45 and with outlet ports 48 which open into a muiier 49.

It has been found, however, that in the prior construction when the pressure fluid is admitted to the tool under reduced pressure, as where the operator wishes to start a cutting operationslowly and carefully, the tool frequently stalls. This results when the piston is moving slowly and reaches substantially the mid-position in its reciprocal vcycle wherein it is in closing relation to both the forward exhaust -ports 44 and the rearward exhaust ports 45. At this time, apparently, the pressure in both the forward. and rear. parts of the piston chamber becomes substantially equal, and the piston lacks sufficient momentum to carry it beyond one set of exhaustv When this state of pressure equalization ports. arises, the disk valve isA held. inoperative bythe ybalance `of pressures developed within the valve chamber 2i.l v

The present invention, therefore, contemplates a construction in which the valve is biased or unbalanced for movement in one direction upon an equalization of pressures on opposite sides` of the piston. Herein, this end is attained by providing. means such as a small axial unbalancing piston which is secured fixedly to the valve disk in any suitable manner that will not distort the thin metal thereof Desirably, the valve may be axially apertured as at 52 and the piston may have a reduced portion 53 which in assembly ts within the aperture and is suitably secured permanently in place.

rTo receive the unbalancing piston U, one face of the valve chamber, herein the rear face, has a bore 54 within which the unbalancing piston fits 1. in fairly snug but freely slidable relation. Communicating with the rear end of the bore 54 is apassage 55 which opens to atmosphere by cornmunicating through the valve casing members I9 and 20 with one of the exhaust passages 41. "i It will be apparent, therefore, that a small though vital area of the valve 26 will remain free of pressure under all conditions during operation, thereby effectually preventing equalization of pressure ,on its oppositey sides even though the B0ffpressure within the piston chamber I2 on oppo` site sides of the piston approaches a state of equalization. Thus, the tool will not stall because the valve, due to its unbalance, will move yrearwardly and restore normal operation of the The invention also contemplates the provision of means for cushioning the handle I8 of the tool against vibrations and recoil shocks developed vbyi the rapidly reciprocating piston I3. Accord- 30-ingly, the handle carries a sleeve 51 which is closed head and sleeve but substantially prevent relative rotary movement thereof. Conveniently, such means may take the form of one or more bosses 58 integral with the rear edge of the head, and in assembly lit-ting within complementary bores 4'0"' 59 in the handle portion at the rear of the sleeve (Figs. 1 and 2).

Transmission of vibrations from the barrel to the handle is prevented by a combination of mechanical and pressure iiuid cushions, one of a these cushions being disposed to absorb those vibrations which act forwardly upon the tool and another cushion being disposed to absorb the vibrations acting rearwardly on the tool. By way of example, the mechanical cushion may be arranged to absorb the forwardly acting vibrations.

For this purpose the sleeve 5l may extend substantially beyond the forward end of the head 2.1 yof the barrel so that suitable resilient means such as a coil spring 60 may be inserted between x? the forwardly extending part of the sleeve and the body of the barrel II) and with its rear end in engagement with the front end of the head. The spring may be maintained under predetermined tension by suitable retaining means vsuch s as a flanged nut 62 threaded into the forward end of the sleeve and having a shouldered recess 63 for receiving the forward end of the spring. Through this arrangement the head 21 is normally maintained in a fixed position with respect @sito the handle, that is, the rear end of the head may normally abut part of the sleeve-enclosing portion of the handle, but vibrations acting forwardly on the tool will be absorbed by the spring.

The rearwardly acting vibrations may be ab 'Jsorbed efectually by one or more pressure uid cushions which may be developed between the rear end of the head 2l and the handle in the operation of the tool. Desirably, this may be accomplished by providing the rear closure of the sleeve 51 with a forwardly projecting plunger,

herein comprising an axial boss Sli which is adapted to fit within the bore of the ring nut 30 and which closely approaches the rear face of the valve casing member I9 in the inoperative condition of the tool. The pressure fluid port 32 may pass through the boss 64 and the forward mouth of the port may open in substantial radially spaced relation to the supply ports 33 in the rear face of the casing member I9. When live pressure uid is delivered through the port 32 to the forward end of the bore, substantial force will be exerted by the iiuid against the rear of the valve casing, such force being substantially augmented by the restriction upon passage of the pressure fluid to the supply ports 33 due to the close proximitir of the forward end of the boss B4 to the rear of the valve casing. Preferably the spring IEB is tensioned to yield a certain amount under the force exerted by the live pressure fluid. thereby allowing the barrel to move forwardly in the sleeve 5l and permitting the development of a live pressure fluid cushion which will absorb vibrations acting rearwardly on the barrel.

Preferably the live iluid pressure cushion is confined in its action to a limited. area of the coacting parts of the device and may be supplemented by an incidental or auxiliary fluid cushion active between the major area between the rear end of the barrel and the handle of the tool. This end may be attained by forming the boss 64 throughout its principal extent of substantially smaller diameter than the internal diameter of the ring nut 36 and interposing a closely fitting packing 65 between the boss and the inner wall of the nut. Preferably, the packing 55 may be formed of leather or other suitable material and is of substantiallyapertured cup-shape with the principal portion of its exterior surface in ccntact with the wall of the bore of the ring nut and its inner edge clamped in xed position adjacent the base of the boss 6A by suitable means such` as a nut 51 threaded upon the boss. The forward edge of the packing may be beveled outwardly as at 68 so that live pressure Huid acting thereon will force the same more closely into sealingrelation. Through this construction the live pressure fluid cushion will be confined to an area of the same diameter as the bore of the ring nut 30.

Contemporaneously with development of the live pressure cushion, the major area of the opposed portions of the rear part of the barrel and the handle are separated, providing `an auxiliary cushion chamber B9 (Fig. 2). A slight vacuum condition is developed in the cushion chamber 69 at the beginning of operation and has a braking or retarding effect on the separating movement of the parts, thereby preventing initial recoil kwhen pressure fluid is rst admitted to the tool.

pressure iiuid that may escape into the auxiliary cushion chamber will thus be vented and prevented from developing pressure which would tend to separate the parts further.

As soon as the supply of live pressure uid is interrupted, the spring 60 acts to return the barrel to its original position, A substantial volume of air will, however, be trapped in the auxiliary cushion chamber 59 and will dissipate slowly, thus causing the barrel to return rearwardly gradually and without recoil or clashing of parts. f

From the foregoing it will be clear that the present invention affords a new and improved pressure iiuiol actuated tool of sturdy and durable construction and which may be constructed very economically of few and relatively simple parts that have been designed and correlated to coact with utmost efficiency to attain exceptionally high speed, smooth and uniform operation. The tool is capable of higher operating speeds than prior devices due to the increased sensitivity of the fluid controlling disk valve and its exceptionally short range of movement. Under no circumstances can the tool stall from equalized internal pressure during any phase of operation, because the permanent unbalancing means coacting with the fluid controlling valve eifectually prevents iiuid pressure balance in the valve mechanism. Of great advantage, moreover, is the novel combination of coacting mechanical and fluid cushions embodied in the tool whereby breakage oi parts due to operating'vibrations is practically eliminated; and the absorption of such vibrations prevents their transmission to the handle of the tool and permits the operator to attain greater accuracy and make a cleaner cut without the physical detriments resulting from recoil and vibration usually attendant upon the use of most prior tools of this character.

I claim as my invention:

l. A pressure fluid operated tool having, in combination, a barrel including a piston chamber with a piston reciprocable therein, the forward end of said barrel being arranged to receive a tool to be impacted by said piston and the rear end of said barrel having means including a valve casing coacting therewith and embodying- Valve mechanism for controlling the movements of the piston, means securing said valve casing in said barrel and having a bore opening rearwardly to expose the rear part of said valve casing, an internally cylindrical member closed at its rear end and movably surrounding the rear end of said barrel, said member having a boss fitting reciprocally in said bore, means normally acting in the inoperative condition of the tool to move said boss toward said rear part of said valve casing, means for delivering pressure fluid to the forward end of said boss, fluid supply ports in said rear 4part of said valve casing substantially restricted from receiving pressure uid due to the normal disposition oi said boss relative to said valve casing, and packing means surrounding said boss and coacting with the wall defining said bore,

ysaid packing means being arranged for substantially preventing escape of pressure iiuid rearwardly from said bore so as to develop a pressure area at the end oi said boss to move the latter in opposition to said normally acting means partially out of said bore and relatively move said barrel and member incident to the delivery of pressure iiuid oi predetermined force.

2. A pressure fluid operated tool having, in combination, a piston chamber with a piston reciprocable therein, and means for controlling the movements of the piston comprising a valve casing at the rear end of the piston chamber and a valve member' in the form of a thin disk of substantial diameter, said casing providing a 75\valve chamber for the valve member having forward and rear faces spaced apart a distance only slightly greater than the thickness of said valve member, means for supplying pressure fluid to said valve chamber on either side of said valve member comprising a supply port adjacent the periphery of said valve chamber, delivery passages communicating at their forward ends with the forward part of said piston chamber and having their rear ends in communication with said valve chamber through said rear face thereof, and means concentric with thelatter ends of said passages and coactive with said valve member for effecting a sealing relation against the entrance of pressure iluid into said passages in one position of said valve, said rear face of said valve chamber having inwardly offset portions of substantial area which remain out of contact with said valve member to provide uid cushions therebetween when the valve is in sealing relation to said passages, whereby to facilitate rapid movement of said valve member away from said sealing relation.

3. in a pressure operated tool of the character described, the combination of a barrel having a longitudinal piston chamber and a piston reciprocal therein, said barrel having al bore'of larger diameter than said chamber coaxial therewith and opening rearwardly, a valve casing seated in the inner end of said bore in closing relation to said chamber and having its outer face substantiallyinwardlyl of the outer end of the bore, said outer face of said casing being apertured to receive pressure iiuid, a ring nut threaded into said bore for holding said valve .casing in place and having a smooth axial bore dimensioned to expose the apertured portion of said outer face of the casing, a handle member movably associated with the rear end of the barrel 'including a fixed forwardly projecting plunger arranged to project movably into said ring nut bore and having a pressure fluid passage communicating with said apertured portion of the casing, and means' providing a seal to prevent escape of pressure fluid rearwardly out of said ring nut bore.

4. A pressure fluid operated tool having, in combination, a barrel cylindrically chambered to provide a piston chamber, a piston reciprocable therein, a handle portion including a sleeve member surrounding a rear portion of said barrel and having an enclosing surface opposing the rear portion of the barrel, an auxiliary plunger projecting forwardly from said surface and having a pressure fluid supply port opening through the forward end thereof, said rear portion of said barrel having an enlarged bore communicating with said piston chamber, means for controlling the movements of the piston comprising a valve casing thinner than lthe depth of said bore seated therein and in closing relation over the rear end oi said piston chamber, and means having a central opening secured in said bore for maintaining said valve casing ixedly in operative position and coacting with said rear end of said barrel to provide with said enclosing surface of said sleeve member a chamber enabling relative reciprocal movement between the sleeve member and the barrel, said plunger extending into said central opening to deliver pressure fluid to said valve controlling means` 5. In a pressure uid operated tool, in combination, a barrel including a piston chamber and a piston reciprocable therein, said barrel being arranged forwardly to receive a tool to be impacted by said piston and having a rearwardly opening recess, valve means for controlling operation of said piston including a housing within said recess having aported rear face offset inwardly relative to the rear end of the barrel,

means enclosing said rear end of the barrel, and

'means for delivering pressure fluid to said valve `means for operating said piston including an axially movable plunger projecting into said re-y cess and having a pressure `fluid delivery port communicating with the space between the for- -Ward end of the plunger and said rear face of said housing means, the ported area'of said rear face being sorelated to said plunger that the passage of pressure fluid to the valve means is controlled proportionately to the size ofv said space as governed by the distance of the forward end of the plunger from said rear face.

6, In a pressure fluid operated tool7 in combination, a barrel including a piston chamber and a piston reciprocable therein; said barrel being arranged at its forward end to receive a tool to be impacted `by said piston, means assembled with the rear part of said barrel providing a valve chamber housing having a rear faceformed with supply ports opening therethrough, a sleeve closed at its rear end and slidably surrounding the rear end portion of said barrel, yieldable means operative normally to maintain the barrel rearwardly in said sleeve, and means for delivering pressure iluid including a port opening forwardly in spaced relation to said supply ports through'a part of the closed end of the sleeve which opposes said rear face, the space between said rear face and the opposing surface of said part affording only restricted communication for the passage of pressure fluid between said ports in the initial operation of the tool and being arranged to permit an increased rate of ilow incident to forward movement of said barrel resulting from the development of pressure in said space in.' opposition to said yieldable means during continued operations ofv the tool.

7. In a pressure iluid operated chipping hammer, a barrel having a reciprocal piston therein, handle means mounted upon the rear end of said barrel for axial movement relative thereto and including a passage for a controllable supply of motive fluid, resilient means normally operative to force said barrel and said handle means together and tensioned to yield responsive to predetermined force acting to separate said barrel and handle means axially, valve means for controlling the supply of motive lluid to said barrel,

and a pair of juxtaposed separable surfaces re-` spectively rigid with said handle means and said barrel and arranged to receive the motive fluid therebetween with a pressure equal to said predetermined force and efect the axial separation of said barrelv and handle means, said surfaces controlling the flow of motive fluid from saidl passage to said valve means as an incident to the separating movement thereof, as a result of which said piston may be actuated progressively from slow to rapid reciprocation where the character of the chipping operation requires a cautious start, and as the pressure of the fluid forces separation of said surfaces a shock absorbing pressure fluid cushion will be developed therebetween to cooperate with said resilient means in relieving the tool of vibration.

8.'In combination in a fluid actuated percussion tool of the character described, a barrel adapted to carry a chipping tool at one end and having a reciprocable piston therein to impact the tool, a handle member coacting with the' rear portion of said barrel for relative axial movement and having means for delivering a controllable supply of motive' fluid, a pair of opposed pressure separable surfaces rigid with said handle member and said barrel respectively for receiving the motive fluid therebetween and controlling the passage thereof to said barrel, resilient means of predetermined tension acting to hold said barrel and said handle member in the relative position wherein said surfaces are close together, said resilient means being yieldable responsive to Y the development vbetween said surfaces of iluid pressures sufficient to overcome said tension and permit separation of said surfaces so as to form a live pressure fluid cushion to resist operating 4vibration of said barrel rearwardlypmeans carried by said barrel for controlling operation of said piston including a chambered casing for receiving the controlled supply of pressure fluid from between saidsurfaces, said casing having a pressure sensitive valve member therein to govern the passage of the motive fluid therethrough responsive to pressure differential arising in the reciprocations of said piston, and means for preventing' a balanced pressure condition. within said casing and barrel which would tend to stall the piston when running slowly at the beginning of a chipping operation.

9. A pressure fluid operated percussion tool comprising, in combination, a barrel having a reciprocal piston therein, handle means mounted upon the rear end of said barrel for relative axial movement and including a passage for a controllable supply of pressure iluid, resilient means normally operative to force said barrel and said handle means together and tensioned to yield responsive to predetermined force acting to separate said barrel and said handle means axially, valve means for controlling the supply of motive fluid to said barrel, a pair of juxtaposed separe ble surfaces respectively rigid with said handle means and said barrel and arranged to receive the pressure fluid therebetween with a pressure equal to said predetermined force to effect the axial separation of said barrel and handle means, said surfaces by their spacing controlling the ilow of pressure fluid from said passage to said valve means so that as the pressure increases whereby to move said surfaces apart in opposition to said resilient means the speed and force of the piston will be increased proportionately, and means for retarding vthe separating movement of said surfaces to insure a smooth and progressive acceleration of the piston from starting to full speed even though the pressure fluid is` initially admitted under full pressure through said passage into the space between said surfaces.

`10. A pressure fluid operated percussion tool of the character described comprising, in combination, a barrel for housing the operating mechanism of the tool, a handle member having a sleeve portion slidably embracing one end of said barrel and a closure portion opposing said end, said barrel and handle member being separable to a limited extent by relative axial movement, means on the inner side of said closure portion and said barrel end to provide two substantially separated chambers when said inner side of said closure portion and said barrel end are separated to said limited extent, resilient means normally operative to force said handle member and said barrel together whereby the spaces of said chambers Will be practically eliminated, said closure portion having a pressure fluid supp-ly passage opening into one of said chambers so that upon the development of sufficient livepressure in said one chamber said barrel and said handle member will be forced apart in opposition to said resilient means while the other chamber-Will develop av Vacuum condition thereinto `retard the separating action, and a vent for said vacuum chamber adapted to be opened only afterseparation tosaid limited extent has'been effected by the pressure fluid in said one chamber.

11. A pressure fluid operated tool having, in combination, a piston chamber with a piston reciprocable therein, andmeans :for :controlling the movements of the piston comprisingfa valve'cas sage communicating at the forwardend'thereof with the forward part of said piston chamber .and having the rear end thereof in communication with said valve chamber through said rear face thereof, a portion of said rear vface surrounding the latter end of said passage and coactive with said Valve memberffor effecting a sealing relation against the entrance of pressure fluid into said passage in one position of said valve, a substantial area of said rear face of said valvechamber'f being recessed to remain out of contact with said valve member to provide a uid cushion-When the valve member is in sealing relation to said passage, and a plurality -of ports communicating through said forward face with the rear end of vsaid piston chamber individually circumscribed by separate raised rims for substantially line contact fluid-sealing relation with said valve member, the area of. said forward face surrounding said rims being in constant communication" with said supp-ly port to expose the face `of the valve ymember to live pressure fluid tending to assist in shifting the valve member from fluid sealing relation with said rims.

ERNEST sHAFF. "'25 

